Glyphosate herbicide harms even GM glyphosate-tolerant soybeans

Date:08-26-2020

Glyphosate herbicide application stresses soybeans – even though they're engineered to tolerate the chemical. Report: Claire Robinson

Scientists have found that spraying with glyphosate-based herbicide triggers unintended effects even in genetically modified soybean varieties resistant to these types of pesticide. They report their findings in a new study published in Environmental Sciences Europe.

The researchers, from GenØk–Centre for Biosafety in Norway and the Federal University of Santa Catarina (UFSC) in Brazil, found severe metabolic disturbances in both stacked (multiple transgene) and single transgene trait GM soybeans caused by exposure to a glyphosate-based herbicide.

The scientists used a molecular analytical method known as transcriptomics, which allows the total profile of gene expression or an organism to be determined. The authors of this new study used transcriptomics to investigate if there were alterations in gene expression patterns following spraying with a glyphosate-based herbicide (Roundup Transorb^®) on the stacked-trait GM soybean Intacta Roundup Ready 2 Pro MON-877Ø1-2 × MON-89788-1, engineered for glyphosate tolerance and to express a Bt toxin insecticide, and on the single-trait GM soybean Roundup Ready MON-Ø4Ø32-6, genetically engineered for glyphosate tolerance.

Both GM soybean varieties are approved in the EU for food and feed use but not for cultivation. They are widely grown by famers in Brazil.

The researchers looked at the gene expression levels of the stacked and single-trait soy varieties 8 hours after application of the dose of Roundup Transorb^® legally permitted in Brazil. The results showed that spraying with the glyphosate-based herbicide caused adverse effects on carbon metabolism and flow, energy metabolism, and photosynthesis, as well as plant defence responses. Oxidative stress (an imbalance in the production of reactive oxygen-based molecules that can lead to DNA, RNA, cell and tissue damage) was found to be induced by herbicide application, as suggested by increased activity of the plants' detoxification system via the important antioxidant molecule glutathione.

The stacked variety had a more intense response to the stress of herbicide application, in that more biochemical pathways were affected.

The results build on previous field evidence of GM soybeans' increased susceptibility to other environmental stressors, including drought and diseases – a susceptibility that appears to be caused by the combination of the GM genes and the herbicide application. This previous evidence is detailed in the new paper.

Reflective of real-farm conditions

The authors of the new study say that their research, which was conducted in the controlled environment of a greenhouse, reflects real-farm conditions for GM soybean production.

Dr Sarah Agapito-Tenfen, a scientist from GenØk and the lead author of the new publication, added that the new study contains important lessons for improving risk assessment: "Since we have found differences between the stacked varieties (which combine two or more transgenes) and with the herbicide exposure, we recommend the regulatory agencies to include these same [molecular analysis] techniques that we have used in this study as a risk assessment criterion."

The authors state in their paper that scientists need to look more closely at the effects of herbicide applications on genetically modified plants in order to ensure their safety for consumption and for the environment.

On the question of food safety, Dr Agapito-Tenfen told GMWatch, “Anti-nutrients found in plant species are usually associated with some kind of stress response to an abiotic [non-living] or biotic [living] stressor. Since we detected a disturbance in the biochemical pathways related to stress response, such as glutathione and redox [balance in oxygen production and utilisation] metabolism, we suggest that a new risk hypothesis should be drawn from the altered pathways. For instance, a quantitative investigation of anti-nutrients and the presence of new anti-nutrients should be performed.”

GM maize similarly affected

An earlier study, which includes Dr Agapito-Tenfen among its authors, similarly found that a GM Roundup-tolerant maize (NK603) showed increased oxidative stress, which was believed to be caused by expression of the glyphosate-tolerance transgene. The maize also showed altered glutathione metabolism when glyphosate-based herbicide was sprayed during cultivation. The authors commented that the increased levels of antioxidant enzymes in the GM plants were likely to be a response to oxidative stress "in order to maintain proper physiological function".

For GMWatch, these studies show that the GM transformation process results in unpredictable and undesirable alterations in the function of many genes. The studies confirm not only that GM plants are not substantially equivalent to their non-GM counterparts, but also that they are especially vulnerable to environmental stresses. The first law of thermodynamics tells us that energy cannot be created or destroyed, but only changed from one form to another. Accordingly, the genetic manipulation of plants to confer certain traits such as herbicide tolerance redirects energy that the plant would normally use to adapt to environmental stresses. Thus the use of genetically manipulated crops can undermine the resilience of farming systems.

The new study:

Zanatta, C.B., Benevenuto, R.F., Nodari, R.O. et al. Stacked genetically modified soybean harboring herbicide resistance and insecticide rCry1Ac shows strong defense and redox homeostasis disturbance after glyphosate-based herbicide application. Environ Sci Eur. 32, 104 (2020). https://doi.org/10.1186/s12302-020-00379-6